Use LogRecord.getMessage to get OLTP body

This improves compatibility with logging libraries that use
`logging.setLogRecordFactory()` or patching to customize the message
formatting of the created `LogRecord`s. It does this by using the
processed `LogRecord`'s `getMessage()` method to get the body text
instead of using `record.msg % record.args`.

Also adds "getMessage" to the list of reserved attributes so if the
customization is done by patching the `getMessage` function on the
`LogRecord` directly (instead of using a subclass), it's not
accidentally treated as an attribute.

opentelemetry-sdk/src/opentelemetry/sdk/_logs/_internal/__init__.py

@@ -438,6 +438,7 @@ def force_flush(self, timeout_millis: int = 30000) -> bool:
         "exc_text",
         "filename",
         "funcName",
+        "getMessage",
         "message",
         "levelname",
         "levelno",
@@ -547,10 +548,7 @@ def _translate(self, record: logging.LogRecord) -> LogRecord:
         if self.formatter:
             body = self.format(record)
         else:
-            if isinstance(record.msg, str) and record.args:
-                body = record.msg % record.args
-            else:
-                body = record.msg
+            body = record.getMessage()
 
         # related to https://github.com/open-telemetry/opentelemetry-python/issues/3548
         # Severity Text = WARN as defined in https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/data-model.md#displaying-severity.